Abstracts Category : Other

Petrography, geochemistry and provenance of Saudi Arabian Palaeozoic sandstones

by Alexander Bassis

The Arabian Peninsula hosts a thick Palaeozoic succession, ranging from the Cambrian through the Permian. It not only contains deposits of the two major Palaeozoic glaciations, but also holds both the major Palaeozoic hydrocarbon source and reservoir rocks. In addition, Palaeozoic sandstones serve as important aquifers. The succession is dominated by highly mature quartz arenites, as seen in thin sections. It is starved of fossils and very uniform in lithology. This creates unique problems for the interpretation of provenance and tectonic setting as well as for stratigraphic correlations. In order to better understand provenance, tectonic setting and stratigraphic relationships, the petrography, major and trace element geochemistry, heavy mineral assemblages and single-grain geochemistry of sandstones were studied. Samples were taken in several field campaigns from two study areas in southern (Wajid area) as well as central and northern (Tabuk area) Saudi Arabia. The data set presented here is the first comprehensive study to cover the entire Palaeozoic succession in both the southern and northern part of the Arabian Peninsula. Tectonic discrimination diagrams suggest that deposition of sandstones took place in an intracratonic setting, which is in accordance with the established model for the evolution of the Arabian Plate. The collisional signal from some samples is a relic from the last stages of the amalgamation of Gondwana, carried into the basin by glaciogenic sediments. Major and trace element geochemistry indicate the Neoproterozoic basement of the nearby Arabian Shield as the most likely source for the detritus. An influx of fresh material, probably sourced from the Shield, did occur in the upper Palaeozoic units of southern Saudi Arabia but did not reach the northern study area. Petrographic and geochemical observations have proven to be unsuitable to assess the influence of sedimentary recycling versus strong weathering and reworking during deposition in highly mature quartz arenites. A (meta-) sedimentary source for the Palaeozoic sandstones could therefore neither be proven nor refuted. Multivariate cluster and principal component analysis of geochemical data revealed significant differences between the two study areas. They further allowed differentiating between the lower and upper parts of the southern Saudi Arabian Palaeozoic succession. The heavy mineral assemblages reflect the mineralogical maturity of the Saudi Arabian Palaeozoic siliciclastics. They are dominated by the ultra-stable phases zircon, tourmaline and rutile. Less stable accessories are apatite, staurolite and garnet. Standard heavy mineral analysis of samples from both study areas reveals distinct changes in provenance. CambrianOrdovician sandstones are first-cycle sediments, probably sourced from the Arabian-Nubian Shield. The overlying, Hirnantian glaciogenic deposits consist of recycled CambrianOrdovician material. DevonianPermian sandstones show a significant influx of fresh basement material, as attested by an increase ofAdvisors/Committee Members: Hinderer, Matthias (advisor), Schth, Christoph (advisor), Henk, Andreas (advisor), Becker, Matthias (advisor).